40i 



SCIENCE. 



[N. S. Vol. XX. No. 508. 



region and upon the lateral regions of the 

 upper portion of the back, conditions found 

 in no other species. These results are at- 

 tributed to the tendency of the body to slide 

 down from the pillow. The distinct lines of 

 parting along the sides of the body on the 

 ventral surface are thought to be possibly 

 attributable to the pressure of the arm as it 

 rests upon the body in sleeping, while the 

 whorl which frequently occurs in this line is, 

 contrary to the general principle earlier set 

 forth as accounting for whorls, attributed to 

 the pressure of the elbow. 



The various methods of dressing the hair 

 are said to account for the considerable va- 

 riety of hair directions on the front of the 

 scalp and the back of the neck. 



The pressure of the clothing over the chest 

 involved in respiratory movements is brought 

 in to exjilain the reversal of hair above the 

 ' sternal angle,' while the sudden diminution 

 of hair at the level of the tops of the shoes is 

 cited as an illustration of disuse and is at- 

 tributed to the constant pressure of the shoe 

 below that level. 



In spite of the fact that the habits of man 

 are so well known, it must be admitted that 

 Kidd's discussion of the critical areas of man 

 is the least complete and satisfactory portion 

 of his book. Not only are some of the ex- 

 planations submitted frankly given as mere 

 conjectures, but many iinportant phenomena 

 are wholly ignored. For example, with the 

 exception of the whorl upon the crown of the 

 head, those which sometimes occur upon the 

 lateral hair-parting of the trunk, and a pair 

 in the pectoral region at the level of the 

 sternal angle, there is no recognition of the 

 many ' Wirbel ' (Voigt's term) either diver- 

 gent, i. e., corresponding to Kidd's whorl, or 

 convergent (Kidd's ' tufts ') which have been 

 so carefully worked out by Voigt and others 

 and shown to be of siich frequent, and in 

 some regions of such constant occurrence upon 

 the human body. Moreover, some of these 

 phenomena correspond exactly in location to 

 those to which Kidd attaches so much impor- 

 tance in his discussion of lower mammals. 

 The axillary divergent Wirbel (a whorl), for 

 example, has been found to be of practically 



constant occurrence in man. Kidd, in dis- 

 cussing the axillary whorl of the horse, says 

 (p. 39) that in this region ' the more passive 

 influences of pressure on the hair or friction 

 are not represented, but it is an area with con- 

 siderable opportunity for the active influence 

 of strong, divergent muscular action to mani- 

 fest itself.' He adds : ' Whorls in this region 

 are so rare outside of the ungulate order that 

 after an extensive search for it in other hair- 

 clad mammals, I have been only able to find 

 two instances in which it was present, and 

 then only in a rudimentary form.' The cases 

 cited are both dogs. 



This statement and the fact that Kidd at- 

 tributes none of the peculiarities of hair direc- 

 tion of man to motor phenomena, show that 

 he was probably unaware of the existence of 

 this, and possibly also of many other whorls 

 and tufts upon the body of man. If aware 

 of their occurrence, then there is a serious 

 and very unfortunate discrepancy in his ex- 

 planations, since these two phenomena are in 

 the early part of the book distinctly attributed 

 to divergent and convergent action, respect- 

 ively, of underlying muscles. 



After the discussion of critical areas in 

 lower animals and in man, Kidd gives by 

 way of summary a chapter on the ' Delimita- 

 tion of Hair Tracts.' These hair tracts are 

 shown to be either (1) primitive or (2) ac- 

 quired, (a) by morphological changes or (b) 

 by use or habit. The whole primitive hair 

 slope is compared to the course of a river 

 which continues unchanged until some ob- 

 stacle interferes with its accustomed flow. 

 These obstacles in the case of the hair stream 

 are the mechanical forces which act upon the 

 gTOwing hair opposing the primitive direction 

 of growth. If the action is sufiiciently con- 

 stant the course of the stream is changed. 

 Thus the hairy coat of a mammal bears an 

 indubitable record of the forces to which it 

 has been exposed. 



The otter is cited as a form in which the 

 hair tracts are wholly primitive, while the ox, 

 horse and especially man show that with in- 

 creasing complexity of form and habits of 

 life come increasing mechanical disturbance 

 of the primitive condition and consequent 



